Forming GaN on silicon wafers is a complex heteroepitaxial process where heterostructures of both compressive and tensile strain alloys (e.g., Al, Ga, In) are grown on silicon films. These compressive and tensile strains can cause bowing or warping of the semiconductor wafer. For example, a compressive strain can result in concave bowing, whereas, a tensile strain can result in a convex bowing.
There is a lattice and thermal mismatch between GaN and silicon. As is known, a lattice mismatch between silicon and GaN causes defects formation on GaN, e.g., too thick GaN can cause unwanted stress which can result in the warp. The thermal mismatch impact, on the other hand, happens after the growth and during the cooling of the wafer. The thermal mismatch between silicon and GaN can, for example, cause warp in silicon, peel off from silicon, and cracks in GaN.
To alleviate or compensate for the bowing, a post growth process is required to relax the strains on the semiconductor wafer (silicon wafer). This can create defects in the semiconductor wafer. Also, since the growth process is typically at a very high temperature (e.g., above 1000° C.), the silicon wafer becomes ductile and can easily be deformed. Also, compressive stress builds up during the growth at high temperature and tensile strain builds up during the cool down process, again resulting in potential warping or bowing of the semiconductor wafer. The bowing and warping of the wafer is amplified when GaN is grown on a 12 inch wafer, for example.